Some fuel cells include a humidifying system to humidify inlet gasses. Humidifying systems are used in fuel cells to increase the average current density of a fuel cell. Inlet gasses require an optimal humidity level to produce the highest average current density possible for a particular fuel cell. One technique for increasing humidity of inlet gasses to reach an optimal level is to transfer moisture from the outlet gasses, which have high moisture content from water produced during the chemical reaction in the fuel cell, to the inlet gasses.
A humidifying system used in a fuel cell system may use a hollow fiber membrane. A hollow fiber membrane provides pores on the inside of the hollow fiber membrane to separate moisture from a gas flow. The moisture of outlet gasses that flows inside the hollow fiber membrane is transferred to the outside of the hollow fiber membrane to humidify inlet gasses flowing on the outside of the hollow fiber membrane.